Positron-Proton Scattering

Browman, A.; Schaerf, C.; Liu, F.

doi:10.1103/physrev.139.b1079

Cited by 56 publications

(64 citation statements)

References 33 publications

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“…Nevertheless, the overall trend in the data reveals a small enhancement in R e + e − at the lower ε values, as illustrated in Fig. 7 (which shows a subset of the data, from the SLAC experiments [31,32]). …”

Section: B 2γ Corrections To Proton Form Factorsmentioning

confidence: 90%

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Two-photon exchange in elastic electron-nucleon scattering

2005

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A detailed study of two-photon exchange in unpolarized and polarized elastic electron-nucleon scattering is presented, taking particular account of nucleon finite size effects. Contributions from nucleon elastic intermediate states are found to have a strong angular dependence, which leads to a partial resolution of the discrepancy between the Rosenbluth and polarization transfer measurements of the proton electric to magnetic form factor ratio, G E /G M . The two-photon exchange contribution to the longitudinal polarization transfer P L is small, whereas the contribution to the transverse polarization transfer P T is enhanced at backward angles by several percent, increasing with Q 2 . This gives rise to a small, < ∼ 3% suppression of G E /G M obtained from the polarization transfer ratio P T /P L at large Q 2 . We also compare the two-photon exchange effects with data on the ratio of e + p to e − p cross sections, which is predicted to be enhanced at backward angles.Finally, we evaluate the corrections to the form factors of the neutron, and estimate the elastic intermediate state contribution to the 3 He form factors.

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Section: B 2γ Corrections To Proton Form Factorsmentioning

confidence: 90%

“…Although the current data on elastic e − p and e + p scattering are sparse, there are some experimental constraints from old data taken at SLAC [31,32], Cornell [33], DESY [34] and Orsay [35] (see also Ref. [36]).…”

Section: B 2γ Corrections To Proton Form Factorsmentioning

confidence: 99%

Two-photon exchange in elastic electron-nucleon scattering

2005

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“…Earlier data from elastic e + p and e − p experiments in the 1960s from SLAC [69,70], Cornell [71], DESY [72] and Orsay [73] gave some hints of a small enhancement of R 2γ at forward angles and low Q 2 , but were in the region (at large ε) where TPE is relatively small and were consistent within errors with R 2γ = 1. Data from the VEPP-3 experiment at Novosibirsk [26,27], taken at energies E ≈ 1 GeV ε values the trend in the data is towards values of the ratio slightly below unity, whereas the calculated dispersive TPE corrections give a ratio that has a small, 1% enhancement above unity.…”

Section: Verification Of Tpe Effectsmentioning

confidence: 99%

Dispersive approach to two-photon exchange in elastic electron-proton scattering

Blunden

Melnitchouk

2017

Phys. Rev. C

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We examine the two-photon exchange corrections to elastic electron-proton scattering within a dispersive approach, including contributions from both nucleon and ∆ intermediate states. The dispersive analysis avoids off-shell uncertainties inherent in traditional approaches based on direct evaluation of loop diagrams, and guarantees the correct unitary behavior in the high energy limit.Using empirical information on the electromagnetic nucleon elastic and N ∆ transition form factors, we compute the two-photon exchange corrections both algebraically and numerically. Results are compared with recent measurements of e + p to e − p cross section ratios from the CLAS, VEPP-3 and OLYMPUS experiments, as well as with polarization transfer observables.

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“…The data points are world data on the ratio R e + e − from Refs. [8,9,[71][72][73][74][75][76][77][78][79][80]. Two recent measurements [8,9] have provided significantly more precise measurements at Q 2 ≈ 1.0 and 1.5 (GeV/c) 2 , providing evidence for non-zero TPE at larger …”

Section: B Ratio Of Positron-proton To Electron-protonmentioning

confidence: 99%

“…[7] (short-dashed magenta line), [29] (long-dashed blue line), [68] (large-dotted black line), and [37] (dashed-dotted black line). The data points are direct measurements of R e + e − [8,9,[71][72][73][74][75][76][77][78][79][80]. For the world data, the measurement and Q 2 value(s) in (GeV/c) 2 are given.…”

Section: Fig 4: (Color Online)mentioning

confidence: 99%

Flavor decomposition of the nucleon electromagnetic form factors at lowQ2

2015

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Background The spatial distribution of charge and magnetization within the proton is encoded in the elastic form factors.These have been precisely measured in elastic electron scattering, and the combination of proton and neutron form factors allows for the separation of the up-and down-quark contributions.Purpose In this work, we extract the proton and neutron form factors from world's data with an emphasis on precise new data covering the low-momentum region, which is sensitive to the large-scale structure of the nucleon. From these, we separate the up-and down-quark contributions to the proton form factors.Method We combine cross section and polarization measurements of elastic electron-proton scattering to separate the proton form factors and two-photon exchange (TPE) contributions. We combine the proton form factors with parameterization of the neutron form factor data and uncertainties to separate the up-and down-quark contributions to the proton's charge and magnetic form factors.Results The extracted TPE corrections are compared to previous phenomenological extractions, TPE calculations, and direct measurements from the comparison of electron and positron scattering. The flavor-separated form factors are extracted and compared to models of the nucleon structure.Conclusions With the inclusion of the precise new data, the extracted TPE contributions show a clear change of sign at low Q 2 , necessary to explain the high-Q 2 form factor discrepancy while being consistent with the known Q 2 → 0 limit. We find that the new Mainz data yield a significantly different result for the proton magnetic form factor and its flavorseparated contributions. We also observe that the RMS radius of both the up-and down-quark distributions are smaller than the RMS charge radius of the proton.

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Positron-Proton Scattering

Cited by 56 publications

References 33 publications

Two-photon exchange in elastic electron-nucleon scattering

Two-photon exchange in elastic electron-nucleon scattering

Dispersive approach to two-photon exchange in elastic electron-proton scattering

Flavor decomposition of the nucleon electromagnetic form factors at lowQ2

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